1. Field of the Invention
This invention relates to apparatus for inspecting the interior wall of a pipe or bore. Such apparatus is frequently referred to as "a borescope" and will be referred to as such herein.
2. Acknowledgement of Prior Art
Borescopes are used for inspection of the interior surface of all types of bore such as bore holes for wells or for mining or the interior bores of pipes. They generally utilize the principle of directing light towards an inner reflecting surface of a bore to be inspected, and monitoring reflected light therefrom. Examples of borescopes utilizing this principle are disclosed in U.S. Pat. No. 4,732,474 to Chikama issued Mar. 22, 1988 and in U.S. Pat. No. 5,088,819 to Storz issued Feb. 18, 1992, U.S. Pat. No. 4,967,092 to Fraignier et al issued Oct. 30, 1990 and in U.S. Pat. No. 4,657,387 to Heising et al issued Apr. 14, 1987. The general principle is also utilized in apparatus for inspecting any reflecting surface. Thus endoscopes for surgically inspecting interior parts of the body cavity of humans and animals may utilize this principle as, for instance, in the endoscopes of U.S. Pat. Nos. 4,241,729 and 3,294,085.
Known borescopes may comprise an optical probe located at the distal end region of an elongate rod or sleeve which is capable of being projected into the bore to be inspected. The probe may be connected to a monitor at the proximal end of the rod or sleeve outside the bore. Light from the probe is directed towards the wall of the bore and reflected light signals are transmitted to the monitor. The longitudinal position of the probe within the bore may be adjustable.
Borescopes of the type just described vary in their efficiency dependent on the radius of the bore whose wall is to be inspected. If the bore is of small radius the path travelled from the optical source to the bore wall and back to the receptor is small and loss of brightness and effect of optical aberrations may be minimal. On the other hand, if the radius of the bore is large the path travelled from the optical source, to the bore wall and back to the receptor is large and appreciable distortions may occur. Moreover, lack of definition may also become a problem.
Considerable effort has been put into the design of optical probes small enough to be used in narrow bores (Heising), or for all round viewing (Fraignier), or for the provision of flexible shafts to extend round pipe or bore bends (Storz).
Optical technology for the inspection of a surface within a pipe or bore and at a considerable distance away from the monitor has become very sophisticated as may be seen from Heising et al and Fraignier et al in respective U.S. Pat. Nos. 4,657,387 and 4,967,092 referred to above. The sophisticated apparatus which is now available may allow for detailed inspection of sectors of inner pipe wall. If, due to the geometry of the pipe and a probe which is rotatable coaxially therein is such that close inspection of the pipe wall is not possible, much of the advantage of the modern technology may be lost. The present inventor has addressed this problem.